Answering a fan's question with a video is better than answering it in 500 characters or less. *LOL* This video describes the newer Maxi-Chamber design, which you'll find on almost every air-brake vehicle today. The older design, a "Roto-Chamber" design, may still be found on antiques. For a view of the Roto-Chamber components refer to the image below; http://www.tpub.com/content/constructiongrader/TM-5-3805-263-14-P-3/0668960279im.jpg